The present invention is related to devices, systems and methods for determination of parameters for a procedure, for estimation of cardiopulmonary function and for fluid delivery, and, particularly, to devices, systems and methods for delivery of a pharmaceutical fluid to a patient based upon estimation of cardiovascular function (for example, cardiac output) of the patient, and, especially for delivery of a contrast medium to a patient during a medical injection procedure.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosure of all references cited herein are incorporated by reference.
The administration of contrast medium (with, for example, a powered injector) for radiological exams typically starts with the clinician filling an empty, disposable syringe with a certain volume of contrast agent pharmaceutical. In other procedures, a syringe pre-filled with contrast agent is used. The clinician then determines a volumetric flow-rate and a volume of contrast to be administered to the patient to enable a diagnostic image. An injection of saline solution, having a volume and flow rate determined by the operator, often follows the administration of contrast agent into the veins or arteries. A number of currently available injectors allow for the operator to program a plurality of discrete phases of volumetric flow rates and volumes to deliver. For example, the SPECTRIS SOLARIS® and STELLANT® injectors available from Medrad, Inc. of Indianola, Pa., provide for entry of up to and including six discrete pairs or phases of volumetric flow rate and volume for delivery to a patient (for example, for contrast and/or saline). Such injectors and injector control protocols for use therewith are disclosed, for example, in U.S. Pat. No. 6,643,537 and Published U.S. Patent Application Publication No. 2004-0064041, the disclosures of which are incorporated herein by reference. The values or parameters within the fields for such phases are generally entered manually by the operator for each type of procedure and for each patient undergoing an injection/imaging procedure. Alternatively, earlier manually entered values of volume and flow rate can be stored and later recalled from the computer memory. However, the manner in which such parameters are to be determined for a specific procedure for a specific patient continues to undergo development.
In that regard, differences in contrast dosing requirements for different patients during imaging and other procedures have been recognized. For example, U.S. Pat. No. 5,840,026, the disclosure of which is incorporated herein by reference, discloses devices and methods to customize the injection to the patient using patient specific data derived before or during an injection. Although differences in dosing requirements for medical imaging procedures based upon patient differences have been recognized, conventional medical imaging procedures continue to use pre-set doses or standard delivery protocols for injecting contrast media during medical imaging procedures. Given the increased scan speed of recently available CT scanners including MDCT (or MSCT) scanners, single phase injections are dominant over biphasic or other multiphasic injections in regions of the world where such fast scanners are used. Although using standard, fixed or predetermined protocols (whether uniphasic, biphasic or multiphasic) for delivery simplifies the procedure, providing the same amount of contrast media to different patients under the same protocol can produce very different results in image contrast and quality. Furthermore, with the introduction of the newest MDCT scanners, an open question in clinical practice and in the CT literature is whether the standard contrast protocols used with single-slice, helical scanners will translate well to procedures using the MDCT machines.
A few studies have attempted quantitative analyses of the injection process during CT angiography (CTA) to improve and predict arterial enhancement. For example, Bae and coworkers developed pharmacokinetic (PK) models of the contrast behavior and solved the coupled differential equation system with the aim of finding a driving function that causes the most uniform arterial enhancement. K. T. Bae, J. P. Heiken, and J. A. Brink, “Aortic and hepatic contrast medium enhancement at CT. Part I. Prediction with a computer model,” Radiology, vol. 207, pp. 647-55 (1998); K. T. Bae, “Peak contrast enhancement in CT and MR angiography: when does it occur and why? Pharmacokinetic study in a porcine model,” Radiology, vol. 227, pp. 809-16 (2003); K. T. Bae et al., “Multiphasic Injection Method for Uniform Prolonged Vascular Enhancement at CT Angiography: Pharmacokinetic Analysis and Experimental Porcine Method,” Radiology, vol. 216, pp. 872-880 (2000); U.S. Pat. Nos. 5,583,902, 5,687,208, 6,055,985, 6,470,889 and 6,635,030, the disclosures of which are incorporated herein by reference. An inverse solution to a set of differential equations of a simplified compartmental model set forth by Bae et al. indicates that an exponentially decreasing flow rate of contrast medium may result in optimal/constant enhancement in a CT imaging procedure. However, the injection profiles computed by inverse solution of the PK model are profiles not readily realizable by most CT power injectors without major modification.
In another approach, Fleischmann and coworkers treated the cardiovascular physiology and contrast kinetics as a “black box” and determined its impulse response by forcing the system with a short bolus of contrast (approximating a unit impulse). In that method, one performs a Fourier transform on the impulse response and manipulates this transfer function estimate to determine an estimate of a more optimal injection trajectory than practiced previously. D. Fleischmann and K. Hittmair, “Mathematical analysis of arterial enhancement and optimization of bolus geometry for CT angiography using the discrete Fourier transform,” J Comput Assist Tomogr, vol. 23, pp. 474-84 (1999), the disclosure of which is incorporated herein by reference.
Uniphasic administration of contrast agent (typically, 100 to 150 mL of contrast at one flow rate) results in a non-uniform enhancement curve. See, for example, D. Fleischmann and K. Hittmair, supra; and K. T. Bae, “Peak contrast enhancement in CT and MR angiography: when does it occur and why? Pharmacokinetic study in a porcine model,” Radiology, vol. 227, pp. 809-16 (2003), the disclosures of which are incorporated herein by reference. Fleischmann and Hittmair thus presented a scheme that attempted to adapt the administration of contrast agent into a biphasic injection tailored to the individual patient with the intent of optimizing imaging of the aorta. A fundamental difficulty with controlling the presentation of CT contrast agent is that hyperosmolar drug diffuses quickly from the central blood compartment. Additionally, the contrast is mixed with and diluted by blood that does not contain contrast.
Fleischmann proscribed that a small bolus injection, a test bolus injection, of contrast agent (16 ml of contrast at 4 ml/s) be injected prior to the diagnostic scan. A dynamic enhancement scan was made across a vessel of interest. The resulting processed scan data (test scan) was interpreted as the impulse response of the patient/contrast medium system. Fleischmann derived the Fourier transform of the patient transfer function by dividing the Fourier transform of the test scan by the Fourier transform of the test injection. Assuming the system was a linear time invariant (LTI) system and that the desired output time domain signal was known (a flat diagnostic scan at a predefined enhancement level) Fleischmann derived an input time signal by dividing the frequency domain representations of the desired output by that of the patient transfer function. Because the method of Fleischmann et. al. computes input signals that are not realizable in reality as a result of injection system limitations (for example, flow rate limitations), one must truncate and approximate the computed continuous time signal.
In addition to problems of control with current injector systems, many such systems lack convenience and flexibility in the manner in which the injector systems is operated. In that regard, the complexity of medical injection procedures and the hectic pace in all facets of the health care industry place a premium on the time and skills of an operator.
In many current quantitative analysis techniques, clinical practicalities thus diminish the chances of adoption into regular use. Physiological models can require the estimation of many physiologic parameters a priori (for example, cardiac output, organ and great vessel blood volumes, permeability factors). The models may not be well oriented towards per-patient adaptation based on test-bolus enhancement because of certain mathematical limitations. Moreover, methodologies in which an impulse response is determined using a short bolus of contrast can be difficult to implement practically because satisfactory means do not exist to easily transfer time-bolus enhancement data between a scanner and an injection system.
Although advances have been made in the control of fluid delivery systems to, for example, provide a desirable time enhancement curve and to provide for patient safety, it remains desirable to develop improved devices, systems, and method for delivery of fluids to a patient.